The present invention relates to a reader/writer and an analog switching circuit. More particularly, it relates to a reader/writer for sending/receiving data to/from the outside in a contactless manner through electromagnetic induction coupling and an analog switching circuit for providing conduction/nonconduction of an analog signal.
Recently developed data carriers include IC chips on which memories and control circuits are integrated so as to be supplied with power from the outside and send/receive data to/from the outside in a contactless manner through electromagnetic induction coupling or the like. An example of such data carriers is a contactless IC tag. A contactless IC tag is characterized by a large storage capacity and high security function. Also, since a contactless IC tag can communicate by bringing the tag itself close to the antenna portion of a reader/writer or inserting the tag into the slot of a reader/writer, there is no need to provide a mechanism unit such as contact, and hence, it can be maintenance-free. Accordingly, a contactless IC tag can be useful for product management and production control and also for component management and characteristic improvement by setting it on a removable component used in equipment. For example, there is a contactless IC tag system in which contactless IC tags are respectively set on a variety of goods so as to store ID numbers and characteristics of the goods in memories included in the contactless IC tags for communicating with a reader/writer in a contactless manner through the electromagnetic induction method.
In the contactless IC tag system, the communication with a plurality of contactless IC tags is performed by any of the following methods:
(a) The plural contactless IC tags are respectively and successively moved close to the antenna circuit part of a reader/writer;
(b) The antenna circuit part of a reader/writer is successively moved close to the respective IC tags;
(c) A plurality of readers/writers are prepared so as to communicate with corresponding contactless IC tags; and
(d) Switches are provided between a transmission circuit and a plurality of antenna circuits of a reader/writer so as to switch the antenna circuits in the communication with the respective IC tags.
In the contactless IC tag system using the method (d), as shown in FIG. 9, a plurality of (herein three) antenna circuits 108 through 110 are provided with respect to a transmission circuit 101 of a reader/writer 100. Between the transmission circuit 101 and the antenna circuits 108 through 110, small signal switches 102 through 104 and high voltage withstanding amplifiers 105 through 107 are respectively disposed. Herein, each of the small signal switches 102 through 104 is a switch for providing conduction/nonconduction of an analog signal at a comparatively low level (for example, an analog signal having amplitude of ±1 V with 2.5 V at the center). An analog signal from the transmission circuit 101 is sent by any of the small signal switches 102 through 104 (for example, the small signal switch 102) to a corresponding one of the high voltage withstanding amplifiers 105 through 107 (for example, the high voltage withstanding amplifier 105) and is amplified by any of the high voltage withstanding amplifiers 105 through 107 so as to be supplied to a corresponding one of the antenna circuits 108 through 110 (for example, the antenna circuit 108).
In the reader/writer 100 of the contactless IC tag system shown in FIG. 9, the high voltage withstanding amplifiers 105 through 107 are respectively disposed at the previous stages of the antenna circuits 108 through 110, which disadvantageously increases the number of components.